Static electricity discharger



June 22, 1965 s. KLEINHANS 3,191,094

STATIC ELECTRICITY DISCHARGER Filed July 27, 1962 United States Patent3,191,09d STATIC ELECTRECETY DES CHARGER Schuyler Kleinhans, SantaMonica, Calif., assignor to Douglas Aircraft Company, Inc, Santa Monica,(Calif. Filed July 27, W62, Ser. No. 212,346 6 Claims. (Cl. 3l7--2 Thisinvention relates to aircraft and is particularly concerned withobviating the detrimental effects of the accumulation and discharge ofstatic electrical charges, at the aircrafts surfaces, on thenavigational equipment, radio apparatus, the ignition system and othersystems of the propulsion plant, upon the fuel contents of the craft andsometimes even upon the structural integrity of the airframe. Thesestatic electrical charges are generated on the surfaces of all-metalaircraft by the friction-creating movement of the craft through theatmos phere or by charges deposited by meteorological precipitation,such as hail, snow and rain, with consequent tribeelectrical phenomenapertaining thereto, resulting in D.C. electricaldischarge-potentialities if the charge builds up to a triggering voltageof about 200,000 volts.

The fact should be here taken into account that such charges can, andoften do, attain a magnitude of several hundred thousand volts, thecharge having, as the particular case may be, either a positive ornegative polarity. Usually the charged body is of negative polarity, andthe particles in the airstream sweeping the body are of positivepolarity. The sudden D.C. discharge of this high-voltage charge may wellinjure the carried personnel, in addition to having the other well-knowndetrimental effects on the radio, radar, and ignition, etc, systems ofthe craft. These factors considered, the topicality and seriousness ofthe conditions alleviated and of the problems solved by the presentinvention can well be appreciated.

Proposals are of record approaching these situations with a view totheir alleviation. Some of them have alleviated one or more aspects ofthese situations by use of primitive trailing wire dischargers,antistatic coatings, equally obsolete needle points at the tail coneapex and the wing tips; the use of triboelectric particles of quartz,and combinations of trailing edge wicks and capacitative meanscooperating therewith to trigger the discharge at a somewhat, butinsufficiently, lowered voltage, the latter constituting the mosteffective means developed to this date.

It was discovered, however, in connection with all these proposals, thatamong other inadequacies, (1) a certain minimum potential difference,usually of the order of several hundreds of thousands of volts, mustbuild up on the body in order to trigger discharge and such discharge isdetrimental, as aforesaid; and (2) the discharge is intermittent, ratherthan continuous.

Concisely stated, the present invention solves these problems byincorporating in, or adjacent, the trailing edge portion of all or aportion of the major components, including lift surfaces, stabilizingsurfaces and control surfaces, of an aircraft or other bodyhavingrelative movement with respect to a meteorological medium, a combinationincluding radioactive means for (1) preventing the build-up, orincremental accumulation, on the surfaces or faces of the components ofthe craft, of the aforementioned ultra-high voltage static charges and aplurality of discharge wicks. In solving these problems the inventionetfectuates a continuous discharge of increments of charge out throughthese wicks and this it does substantially as soon as they aregenerated. This means that the charge is discharged at a relatively lowpotential, far below the aforestated magnitudes. The radioactive meansare associated with trailing-edge wicks in any suitable structuralmanner and the radioactive means may be of that kind which emit alpha,or beta, or gamma rays, or all of them simultaneously. The wicks, hereinassumed to be of the conventional type, have naturally a high-gradientas to their potential, and tend, even in the conventional device, toleak 01f electrons and ionize the air but only in their immediatevicinity and only at 200,000 volts. The radioactive ionized airstreamultimately combines with the wick-ionized particles in which the wicksare immersed.

One of the prototype physical embodiments incorporating the presentinvention is representationally shown in the accompanying drawing,forming an integral part of this disclosure. it is to be understood,however, that these drawings and the following detailed description ofthe construction depicted therein, are presented merely by Way ofexample and are not to be taken as constituting the sole mode andstructural means for giving effect to the inventions concepts andobjectives. For, the invention contemplates any and all means,equivalent to the exemplificatory means chosen for detailing herein,that fall within the scope of the subjoined claims.

In this drawing:

FIGURE 1 is a somewhat diagrammatic, fragmentary chordwise section of aportion of an airfoil that incorporates the principles of the invention;

FIGURE 2 is a diagrammatic, fragmentary perspective view of a portion ofan airfoil embodying the invention; and

FIGURE 3 is a view, similar to that of FIGURE 1, showing acuatedischarge electrodes substituted for the wicks of FIGURE 1.

Referring now in general outline to the specific, but not limitative,construction shown in the drawing, the invention comprises, broadlystated, the combination with the trailing-edge portion 10 of a metallicairfoil, such as a lift-surface, a stabilizing surface or a controlsurface, of a plurality of wicks, tufts, or the like 12, composed of amaterial that is preferably, but not limitatively, only semi-conductive;and a small, but adequate, mass, capsule or block 14 of a radioactivematerial disposed inside the airfoil ahead of the trailing edge.Preferably this material is one of the radioactive isotopic chemicalelements which emits radioactive particles, including beta particles,such as americium 242, by way of example. The invention does notexclude, however, the employment of a radioactive material which emits,among other decay-products, alpha or gamma particles, such as curium244, radium 226, polonium 210, etc.

In either case, the function of the mass 14, is solely by theradioactivity of the isotope 14, to ionize the ambient air at theairfoils trailing edge portion 15. The nature of this phenomenon issimilar to that occurring upon passage of an electrical current throughan electrolyte, whereby each of the atoms of the electrolyte has anelectron added to or removed therefrom, converting the atoms into ions.

The object of ionizing the air at and aft of the trailing edge region ofthe airfoil is to reduce the electrical resistance of the ambient airthereat, for ionized air is of reduced resistivity and is a satisfactorymedium for inducing or triggering the continuous discharge of a chargeof static electricity from a moving body immersed in air.

- This is true whether the static charge is generated by skin frictionof the airfoil with the ambient air or is created by precipitationimpinging upon an airfol and the deposition of its electrical charge, oreither polarity, thereupon.

The plurality of tufts, or wicks, 112, each comprises, as isconventional, a plurality of strands, filaments, or elongate pieces ofeither conductive, or semi-conductive material. Each wick or the like isfixedly mounted, in any suitable manner, as indicated in rrounn 2, tothe trailing edge of the airfoil along its spanwise dimension, the wickslying in equidistantly spaced relationship with each other. The wicksextend in chordwise attitude, and conically enlarge, or flarerearwardly. The static-electricity space charge pattern around the wicksis not of essential importance, but in order to demonstrate the noveldecoupling effect of the invention on the spacefield charge, a patternis illustrated in FIGURE 1 and is described hereinafter.

The wicks or tufts may be anchored, at their inner ends, to the airfoilor other portion of the charged body in any desired, or suitable manner,as disclosed, for example, in the patent to R. Beach, No. 2,497,924. Or,they may merely be inserted between the upper and lower skins of thetrailing edge before riveting these skins together, the riveting thenfirmly clamping the inner ends of the wicks in place, although a slightand harmless bulge at each wick anchorage may result from the employmentof this technique. Preferably however, each wick is looped on itself anda wide keeper inserted through the loop. See FIGURE 2.

The Wicks may, or may not, be physically directly connected to the mass14, as desired, although direct contact is not essential. Further, if amass 14 should happen to be located closely adjacent a human occupant ofthe craft, or adjacent to other organic tissue, the face of theradioactive material closest to an occupant may be suitably shielded, asshown in FIGURE 1, especially for long flights in the course of which hemay otherwise be continuously exposed to and affected by, the beta,alpha or gamma particles, with obvious consequences. Such shielding maybe in the form of a lead box, plate, or the like, shown in FIGURE 1,thus to exclude the possibility of damage to the occupant from theparticles radiated from the radioactive material.

As shown in FIGURE 1, the space charge-fields of the airfoilsdischarging locus 16 and of the electrostatic field 17 of the wicks ortufts are effectively decoupled by this arrangement. At 18 is shown atypical null region of the wick, this null locus being so positioned bythis invention and so decoupled from the other field that theradio-frequency components in this electrical discharge are effectivelyreduced. The radio, radar, and other such apparatus in the craft arerelieved of the usual interference therewith occasioned by the staticcharge and discharge thereof.

This effect is attributable to the fact that the usual sharp peak of thecurrent-curve of the discharge is attenuated, or even flattened, bymeans of this invention. It may be found under certain conditions that,to establish absolute ole-coupling, the trailing edge portion of theairfoil may be well overlaid in this portion with a plastic, or othernon-conductor, the effects of such arrangement being well-known in theart.

As shown in FIGURE 3, instead of wicks, a plurality of pointed metallicelectrodes, 20, depicted as being directed rearwardly, but alsosusceptible of orientation in an upward direction, as desired, may beemployed.

It is worthy of recitation that the present invention may wellincidentally serve to reduce the attraction of the body for lightning.This it does by virtue of the fact that the novel discharge arrangementmaintains a relatively low potential level, but, one nonetheless higherthan that of the usual lightning attractors, on the surface otthe body,thereby to reduce the bodys attraction 4 for lightning bolts, the bodyalso having the same polarity as that of the bolts, ordinarily. Also,there are few, if any, sharp points on the body to attract the bolts.

Although certain specific materials, structures and arrangements havebeen recited hereinabove, it is to be understood that the invention isby no means restricted in its scope and in its possible embodimentsbecause of the recitation of the foregoing parameters and specificterminology, which are presented merely to render the concepts moreconcrete.

I claim:

- 1. In combination:

a body having, with a meteorological medium, relative movement, therebeing established on at least one face thereof a charge of staticelectricity by virtue of the immersion and relative movement of the bodywith respect to the meteorological medium; and

radioactive means disposed in adjacency with a trailing region of saidface and emitting radioactive particles ionizing the air adjacent saidregion and continuously discharging said charge through the ionized airsubstantially instantaneously upon the generation of the charge;

accumulation of static electricity on said face hence failing to occur.l

2. A combination in accordance with claim 1, in which said radioactivemeans comprises material that emits radioactive particles includingalpha-particles.

3. A combination in accordance with claim 1 in which said body is anall-metal aircraft and in which said face constitutes one of theexternal struc tural boundaries of an airfoil.

A combination according to claim 1, in which said radioactive meanscomprises radioactive polonium, or 21o 5. A combination in accordancewith claim 1, in which said radioactive material emits radioactiveparticles including beta-particles.

6. In a system useful in providing a continuous low potential dischargepath for static electrical charges normally accumulated on a conductivebody upon relative movement between said body and a meteorologicalmedium, the combination of:

passive charged-particle emitting means carried by said body forproviding a supply of ions;

said ions serving to ionize elements of said meteorological medium; and

low electrical potential discharge means carried by said body; and

extending therefrom in substantially the direction of movement of andfor intersectionby said ionized elements;

said ionized elements defining a continuous low po tential dischargepath for said static electrical charges between said body and saiddischarge means.

References Qited by the Examiner UNITED STATES PATENTS 2,732,517 1/56Alabaster 317--2 2,794,118 5/57 Kiriloff 317-2 2,933,732. 4/ 60' Tanner3 l7-2 2,972,680 2/61 Hicks et al. 25044 3,106,663 10/63 Tanner 3172SAMUEL BERNSTEIN, Primary Examiner.

1. IN COMBINATION: A BODY HAVING, WITH A METEROLOGICAL MEDIUM, RELATIVEMOVEMENT, THERE BEING ESTABLISHED ON AT LEAST ONE FACE THEREOF A CHARGEOF STATIC ELECTRICITY BY VIRTUE OF THE IMMERSION AND RELATIVE MOVEMENTOF THE BODY WITH RESPECT TO THE METEOROLOGICAL MEDIUM; AND RADIOACTIVEMEANS DISPOSED IN ADJACENT WITH A TRAILING REGION OF SAID FACE ANDEMITTING RADIOACTIVE PARTICLES IONIZING THE AIR ADJACENT SAID REGION ANDCONTINUOUSLY DISCHARGING SAID CHARGE THROUGH THE IONIZED AIRSUBSTANTIALLY INSTANTANEOUSLY UPON THE GENERATION OF THE CHARGE;ACCUMULATION OF STATIC ELECTRICALLY ON SAID FACE HENCE FAILING TO OCCUR,